The invention relates to switching power supply (SPS) receiving AC line voltage or DC voltage, particularly for power supply systems requiring high output power and high efficiency.
Half bridge SPS is capable of providing high output power and has high efficiency. In particular, voltages of opposite polarities are successively applied across a single primary winding of a power transformer, wherein only two transistors are employed. An input voltage is stored in a pair of capacitors coupled in series, whereby an effective capacitance is halved. Moreover, a ratio of voltages stored in the capacitors depends on the capacitance ratio thereof. Values of the capacitors are unequal and therefore voltages stored therein have unequal values. Adequate switching times of the transistors must be considered in order to reduce flux symmetry problems and avoid transformer saturation. The imbalance in operating flux level is further reduced by a capacitor which is coupled in series with the primary and must sustain AC voltage and high current.